It is well known in the art that wells in sandy, oil-bearing formations are frequently difficult to operate because the sand in the formation is poorly consolidated and tends to flow into the well with the oil. This "sand production" is a serious problem because the sand causes erosion and premature wearing out of the pumping equipment and the like and is a nuisance to remove from the oil at some later point in the production operation. In some wells, particularly in the Saskatchewan area of Canada, the oil with the sand suspended therein must be pumped into large tanks for storage so that the sand can settle out. Frequently, the oil can then only be removed from the upper half of the tank because the lower half of the tank is full of sand. This, too, must be removed at some time and pumped out. Moreover, fine sand is not always removed by this method and this causes substantial problems later in the production run and can even lead to rejection of the sand-bearing oil by the pipe line operator. Accordingly, it has been a well recognized need of the art for some time to provide methods whereby sand production can be avoided in wells of this kind.
Two prior art approaches are shown in U.S. Pat. Nos. 3,951,210 to Wu et al., and 3,003,555 to Freeman et al. These patents both utilize the characteristics of the crude oil found in the sand formation for provision of a semi-solid yet permeable block to the production of sand. Freeman et al use steam in a sealed section of the wall to burn off the lighter ends and to cause the heavier portion of the crude oil, largely carbonaceous material such as asphaltenes to be consolidated in the sand surrounding the well, so as to provide a semi-solid permeable block to the sand. However, such methods are unduly complex and difficult to implement, particularly with respect to the fact that there is a distinct shortage of skilled labor available to perform such tasks.
If anything, the approach of Wu et al is more complicated because it uses solvents as well as steam to separate the asphaltenes from the remainder of the crude oil and to cause them to precipitate to form the hard, permeable sand barrier. Accordingly, this method is not as useful as it might be, although as does Freeman, Wu shows the useful concept of using some component of the crude oil to itself form a block to the production of sand, and shows the concept of separating this portion from the remainder of the crude oil in situ. The present invention follows both of these broad concepts.